On 7 Mar 2006 06:04:13 -0800, "mazerom"
wrote:

how accurate can we get with doppler shift when we have a digitally
modulated signal as its source?compared to a unmodulated CW signals
which has a tone frequency,whats the reliability of an FSK signal?

Hi OM,

You've got too many factors running through this. For one, digitally
modulated is not digital data mode (FSK). There are a world of
modulation types and some are strictly derived from a bit stream (not
all bits equal in width either). Sometimes even the carriers are
digitally derived (not a sine wave).

Doppler is going to give rise to dispersion (often a term confined
these days to fiber optics, but whose derivation arose from waveguides
- LF Optics).

73's
Richard Clark, KB7QHC

exactly sir but im referring to the spectral content of the signal its
carrier and sidebands for that matter.how significant will be the
doppler shift of its spectral components other than its carrier
signal?thanks

What's the formula for Doppler shift? Why would you think it does not
apply exactly to all the spectral components of your signal? Do you
think you are dealing with a nonlinear system when you combine doppler
shift with a complex signal?

Cheers,
Tom


mazerom wrote:
exactly sir but im referring to the spectral content of the signal its
carrier and sidebands for that matter.how significant will be the
doppler shift of its spectral components other than its carrier
signal?thanks

mazerom wrote:

exactly sir but im referring to the spectral content of the signal its
carrier and sidebands for that matter.how significant will be the
doppler shift of its spectral components other than its carrier
signal?thanks


Doppler shift is applicable to all frequency components of a signal.

It is a percentage change of the base frequenc[ies] as a function of the
rate of closure or divergence between an observer and the originator of
the signal.

So, for FM it applies to the carrier frequency at ONE doppler shifted
value. It applies to the individual frequency [secondary] components as
another doppler shifted component for each frequency. In practice, the
doppler shifted frequenc[ies] among the secondary components are
extremely small when compared to the prime frequency.

For spread spectrum, it is applicable to ALL frequencies.
For AM, it is applicable to ALL frequencies.
For SSB, it is applicable to ALL frequencies.
For CW it is applicable to ALL frequencies
For FM/NBFM/WBFM, it is applicable to ALL frequencies.
For unmodulated carriers, it is applicable to ALL frequencies.
For audio, it is applicable to ALL frequencies.
For ...., it is applicable to ALL frequencies.

how can you say that seconday components are "EXTREMELY SMALL"
compared to the prime frequency when your signal is in fact a
broadband?
and you forgot one;
For UWB,it's applicable to ALLLLLL frequencies

On 7 Mar 2006 16:29:45 -0800, "mazerom"
wrote:

.how significant will be the
doppler shift of its spectral components other than its carrier
signal?thanks

How much dispersion can you tolerate? "Significance" is an emotional
measure (which is to say it isn't a measure at all). If you cannot
quantify what you mean by this, no one can offer how significant it
is. I've a career of measuring very small differences out to 12
places. What was significant to me was a matter of utter indifference
to 99.999999% of the population - if that many.

73's
Richard Clark, KB7QHC

kb7qhc wrote, "Doppler is going to give rise to dispersion..."

Doppler alone? Care to elaborate on that?

On 8 Mar 2006 12:04:22 -0800, "K7ITM" wrote:

kb7qhc wrote, "Doppler is going to give rise to dispersion..."

Doppler alone? Care to elaborate on that?

What do you mean by doppler alone?

Consider the case of an EM source moving away from you at constant
velocity, with nothing but you with your measurement system, the EM
source, and freespace. What gives rise to dispersion?

K7ITM wrote:

Consider the case of an EM source moving away from you at constant
velocity, with nothing but you with your measurement system, the EM
source, and freespace. What gives rise to dispersion?


There is a small dispersion caused by the modulation scheme. The
modulating frequencies are slightly different from the carrier frequency
and therefore have slightly different doppler shift.

Restated: the Doppler shift on a 144.500 MHz carrier is different from
the Doppler shift on a 15 KHZ FM signal. How much? That's an exercise
for the student ... so sez my Prof!!

The doppler shift of 144.500 MHz is different from the doppler shift of
a 144.515 MHz sub carrier. If the FM moves the sub carrier doppler moves.